Tire forming mold and pneumatic tire producing method using the same

ABSTRACT

Provided are a tire forming mold which enables damage on ribs and blocks of a tire to be effectively prevented when the tire is removed from the tire forming mold in spite of a simple structure thereof, and a pneumatic tire producing method using the same. The tire forming mold according to the present invention is a two-division type of tire forming mold, including a mold main body for forming one side of the tire, wherein the mold main body is provided with a movable part which constitutes a part of a tread forming surface in the direction of the circumference thereof while the tire forming mold is being closed, and which can be moved while the tire is being removed from the tire forming mold.

This application is a divisional Application of Ser. No. 10/991,144,filed Nov. 18, 2004, now U.S. Pat. No. 7,234,927, the entire contentsbeing incorporated by reference. This application claims priority basedon Japanese Patent Application No. 2003-390196, filed Nov. 20, 2003, theentirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a two-division type of tire formingmold and a pneumatic tire producing method using the two-division typeof tire forming mold. More specifically, the present invention relatesto a tire forming mold which prevents damages on a rib and a blockeffectively in spite of a simple structure thereof when the tire isremoved from the tire forming mold, and to a pneumatic tire producingmethod using the tire forming mold.

A two-division type of tire forming mold has heretofore been used in aprocess of curing a tire. Such a two-division type of tire forming moldincludes a molding surface for molding one side of the tire integrally,and has a simple structure. This has brought up an advantage that costsfor related facilities are small. However, in the two-division type oftire forming mold, the tire needs to be separated from the mold in thedirection of the tire axis in a state where groove forming ribs arrangedon a tread forming surface engage with tread portions. For this reason,there may be a case where parts of the ribs and blocks are damaged whilethe tire is separated from the mold.

FIGS. 7( a) to 7(c) schematically show how to remove the tire from thetwo-division type of tire forming mold when the tire has been cured byuse of the tire forming mold. FIG. 8 shows a state of the rib and blockof the tire when the tire is removed from the tire forming mold. In FIG.7( a), a mold division position X for dividing a lower half 21 and anupper half 22 of the tire forming mold is set at a position higher thanthe center line L of the tire T. After completion of curing, the upperhalf 22 of the tire forming mold is displaced upward to open the tireforming mold, as shown in FIG. 7( b). At this time, the tire T remainsin the lower half 21 of the tire forming mold, since the mold divisionposition X is set at a position higher than the center line L of thetire T. Subsequently, as shown in FIG. 7( c), the tire T is pushed up inthe direction of the tire axis, thereby separating the tire T from thelower half 21 of the mold. Then, the tire T is transferred outward inthe direction of the tire diameter. Here, it should be noted that grooveforming ribs are formed on the tread forming surfaces respectively ofthe lower half 21 and the upper half 22 of the tire forming mold. Forthis reason, when the tire T is separated from the lower half 21 of thetire forming mold, ribs and blocks which have been formed in the treadportions of the tire T are deformed as shown in FIG. 8. The rootportions of some of the ribs and blocks to which the largest stress isapplied are ripped, and the ribs and blocks are damaged.

In order to prevent such damages on the ribs and blocks, it has beensuggested that a plurality of sector molds for forming the treadportions are provided separately from the lower and upper halves of thetire forming mold, and that these sector molds are displaced outward inthe direction of the tire diameter when the tire is removed from thetire forming mold (see Japanese Patent Laid-open Official Gazette No.2001-129831, for example). However, the sectional type of tire formingmold using the sector molds has a disadvantage that the sectional typeof tire forming mold increases costs for related facilities to a largeextent.

As other measures, change in the tread compound and modification in theshape of the grooves have been proposed. However, in a case where thetread compound is changed and the shape of the grooves is modified, thismakes it difficult to achieve performance required for the tire. Inaddition, processing application has been proposed. Such processingapplication includes the coating of the inner surface of the tireforming mold with silicone resin, and vapor deposition of fluororesin onthe inner surface of the tire forming mold. However, these cases requiremaintenance services to be performed continuously, since the coatedresins do not have sufficient endurance.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a tire forming moldwhich can make it possible to prevent damages on a rib and a blockeffectively in spite of a simple structure thereof when the tire isremoved from the tire forming mold. Another object of the presentinvention is to provide a pneumatic tire producing method using the tireforming mold.

A tire forming mold according to the present invention for achieving theaforementioned objectives is a two-division type of tire forming mold,which includes a mold main body for forming one side of a tire,characterized in that the mold main body is provided with a movable partwhich constitutes a part of a tread forming surface in the direction ofthe circumference thereof while the tire forming mold is being closed,and which can be moved while the tire is being removed from the tireforming mold.

According to the present invention, the mold main body is provided withthe movable part, which constitutes a part of the tread forming surfacein the direction of the circumference thereof while the tire formingmold is closed, and which can be moved while the tire is separated. Forthis reason, the tire is easy to be locally separated from the tireforming mold in the movable part. Consequently, this can preventconcentration of stress on the tread portion of the tire, which iscaused due to a groove forming rib arranged on the tread formingsurface. Accordingly, a rib and a block can be effectively preventedfrom being damaged when the tire is removed. In addition, the movablepart may only constitute a part of the tread forming surface in thedirection of the circumference thereof, and the movable part requires nospecial power. For this reason, the structure of the tire forming moldas a whole is simple. This enables an inexpensive tire forming mold tobe provided, and enables costs for related facilities to be inhibitedfrom increasing to a large extent.

In the present invention, it is preferable that the measurement of themovable part be one eighth to a half of the circumferential length ofthe tread forming surface. This makes it easy to separate the tire fromthe tire forming mold. In addition, while the tire forming mold is beingclosed, the movable part needs to be fixed to the mold main body. Forthis reason, the behavior of the movable part may be restricted by atightening force of the other half of the tire forming mold, the otherhalf being opposite to the movable part while the tire forming mold isbeing closed. For the same reason, it is preferable that a contactsurface of the movable part with the mold main body, the contact surfaceextending in the direction of the tire diameter, be inclined in a waythat the inner in the direction of the tire diameter a point on thecontact surface is, the outer in the direction of the tire axis thepoint on the contact surface is.

As a structure by which the movable part is fitted to the mold mainbody, the followings can be adopted. First, the movable part can bemounted swingably around a rotating shaft orthogonal to the direction ofthe tire axis. In this case, the rotating shaft of the movable part maybe arranged outward of a dividing position on the inner surface of thetire forming mold, where the mold main body and the movable part aredivided, in the direction of the tire axis. Second, the movable part canbe mounted slidably along an inclined surface which is inclined withrespect to the direction of the tire axis. Third, the movable part canbe mounted slidably along an inclined surface which is inclined withrespect to the direction of the tire diameter. In any one of thesecases, the movable part is displaced in a natural manner in response tothe displacement of the tire.

According to the present invention, the pneumatic tire producing methodis provided, by which the tire is cured by use of the aforementionedtire forming mold, and by which the cured tire is removed from the tireforming mold including the movable part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a tire forming mold according to a firstembodiment of the present invention.

FIG. 2 is an end view shown in a cross-section taken along the lineII-II of FIG. 1.

FIG. 3 is an end view showing a tire forming mold according to a secondembodiment of the present invention, shown in a cross sectioncorresponding to FIG. 2.

FIG. 4 is an end view showing a tire forming mold according to a thirdembodiment of the present invention, shown in a cross sectioncorresponding to FIG. 2.

FIG. 5 is an end view showing a tire forming mold according to a fourthembodiment of the present invention, shown in a cross sectioncorresponding to FIG. 2.

FIG. 6 is an end view showing a tire forming mold according to a fifthembodiment of the present invention, shown in a cross sectioncorresponding to FIG. 2.

FIGS. 7( a) to 7(C) are schematic diagrams showing how to remove a tirefrom a conventional two-division type of tire forming mold in a casewhere the tire has been cured by use of the conventional two-divisiontype of tire forming mold.

FIG. 8 is a cross-sectional view showing the state of a rib and a blockof the tire when the tire is removed from the conventional two-divisiontype of tire forming mold in a case where the tire has been cured by useof the conventional two-division type of tire forming mold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed descriptions will be given of a configuration according to thepresent invention with reference to the accompanying drawings.

FIGS. 1 and 2 show a tire forming mold according to a first embodimentof the present invention. As shown in FIGS. 1 and 2, the tire formingmold according to the present embodiment has a structure in which amovable part 3 is provided in a mold main body 2 including a cavity 1for forming one side of a tire from a bead portion to a tread portion ina integral manner. This movable part 3 is configured to constitute apart of a tread forming surface 4 in the direction of the circumferencethereof while the tire forming mold is being closed, and is configuredto behave independently of the mold main body 2 while the tire is beingseparated from the fire forming mold. In addition, the tread formingsurface 4 is provided with a plurality of groove forming ribs 5 aextending in the direction of the tire circumference and a plurality ofgroove forming ribs 5 b extending in the direction of the tire width.These groove forming ribs 5 a and 5 b are formed on the movable part 3.

It is preferable that the measurement of the movable part 3 is set atone eighth to a half of the circumferential length of the tread formingsurface 4. More preferably, the measurement of the movable part 3 is setat one third to a half of the circumferential length of the treadforming surface 4. In other words, as shown in FIG. 1, the movable part3 is formed by an angle θ around the tire axis in a range of 45° to180°, more preferably in a range of 120° to 180°. If the measurement ofthe movable part 3 is out of the aforementioned range, it is difficultto separate the tire T from the tire forming mold.

A structure in which the movable part 3 is fitted to the mold main body2 is as follows. Specifically, the mold main body 2 includes a hollowportion 6 in a part of the tread forming surface 4 in the direction ofthe circumference thereof, the hollow portion 6 being one in which themovable part 3 is arranged. A rotating shaft 7 orthogonal to thedirection of the tire axis is arranged pivotally in the hollow portion 6of the mold main body 2. The movable part 3 is fitted swingably aroundthis rotating shaft 7 in the hollow portion 6 of the mold main body 2.In addition, the movable part 3 is designed to be displaced freelywithout a power between a position (shown by a solid line) where thetire forming mold is closed and the other position (shown by a brokenline) where the movable part 3 is positioned when the tire is separatedfrom the tire forming mold.

In particular, it is suitable that the rotating shaft 7 of the movablepart 3 be positioned outward of a dividing position on the inner surfaceof the tire forming mold, where the mold main body 2 and the movablepart 3 are divided, in the direction of the tire axis. In FIG. 2, therotating shaft 7 of the movable part 3 is arranged in a position awayfrom the dividing position between the mold main body 2 and the movablepart 3 by a distance D outward in the direction of the tire axis. Inthis point, it is suitable that the distance D be set at 10 to 40 mm.Thereby, the movable part 3 is easy to lean outward in the direction ofthe tire diameter by a force to be generated while the tire T is beingremoved from the tire forming mold.

The movable part 3 is formed so that it is flush with the mold main body2 at the mold dividing position in a state where the tire forming moldis closed. For this reason, the behavior of the movable part 3 isrestricted by a tightening force of the other half of the tire formingmold, the other half being opposite to the movable part 3 while the tireforming mold is being closed. In other words, the movable part 3 isfixed with respect to the mold main body 2 in a state where the tireforming mold is closed.

A contact surface 8 of the movable part 3 with the mold main body 2, thecontact surface extending in the direction of the tire diameter, isinclined in a way that, the inner in the direction of the tire diametera point on the contact surface is, the outer in the direction of thetire axis the point on the contact surface is. It is suitable that anangle of inclination of the contact surface 8 with respect to thedirection of the tire diameter be 15° to 35°. In a case where thecontact surface 8 of the movable part 3 is inclined in this manner, themovable part 3 is energized inward in the direction of the tire diameterwhen the movable part 3 receives a tightening force from the other halfof the tire forming mold. Thereby, the movable part 3 is brought intoclose contact with the mold main body 2 without creating an intersticeon the inner surface of the tire forming mold.

Next, a description will be given of a curing method in which theaforementioned tire forming mold (lower half of the tire forming mold)is used. First, a tire T which has not been cured yet is inserted in thecavity 1 of the mold main body 2. Thereafter, the tire T is covered withthe other half of the tire forming mold (upper half of the tire formingmold), and the lower and upper halves of the tire forming mold arefastened together. At this time, the movable part 3 is fixed withrespect to the mold main body 2 by the tightening force of the otherhalf of the tire forming mold. Thereby, a state that the movable part 3complements the tread forming surface 4 (shown by the solid line) isbrought about. The other half of the tire forming mold is removed aftercompletion of curing, and the tire T which has been cured is elevated.At this time, the movable part 3 is released from the tightening forcewhich the movable part 3 has received from the other half of the tireforming mold, and the movable part 3 is in a movable state. For thisreason, the movable part 3 swings around the rotating shaft 7 as thetire T is elevated upper. In other words, the tire T is easy to belocally separated from the lower half of the tire forming mold in thearea of the movable part 3. As a result, this can prevent concentrationof stress on the tread portion of the tire T, which is caused due to thegroove forming ribs 5 a and 5 b arranged on the tread forming surface 4.Accordingly, the ribs and blocks of the tire can be effectivelyprevented from being damaged when the tire is removed.

FIG. 3 shows a tire forming mold according to a second embodiment of thepresent invention. The present embodiment is carried out by modifyingthe structure by which the movable part is fitted to the mold main body.In FIG. 3, the same reference numerals are affixed to constituentcomponents which are the same as those in FIGS. 1 and 2 and detaileddescriptions for such constituent components will be omitted.

In FIG. 3, the structure by which the movable part 3 is fitted to themold main body 2 is as follows. Specifically, the mold main body 2includes the hollow portion 6 in a part of the tread forming surface 4in the direction of the circumference thereof, the hollow portion 6being one in which the movable part 3 is arranged. The rotating shaft 7orthogonal to the direction of the tire axis is arranged pivotally inthe hollow portion 6 of the mold main body 2. The movable part 3 isfitted swingably around this rotating shaft 7 in the hollow portion 6 ofthe mold main body 2. In addition, the movable part 3 is designed to bedisplaced freely without a power between a position (shown by a solidline) where the tire forming mold is closed and the other position(shown by a broken line) where the movable part 3 is positioned when thetire is separated from the tire forming mold. Incidentally, theplurality of groove forming ribs 5 a extending in the direction of thetire circumference and the plurality of groove forming ribs 5 bextending in the direction of the tire width are arranged in the treadforming surface 4. Out of those, the groove forming ribs 5 a are formedin the movable part 3, and the groove forming ribs 5 b are formed in themold main body 2.

The present embodiment causes the groove forming ribs 5 a extending inthe direction of the tire circumference to belong to the movable part 3,and, on the other hand, causes the groove forming ribs 5 b extending inthe direction of the tire width to belong to the mold main body 2.However, the present embodiment can obtain the same operation and effectas the first embodiment does. Specifically, the groove forming ribs 5 bextending in the direction of the tire width is less prone to become acause of damage on the ribs and blocks. For this reason, the grooveforming ribs 5 b can be removed from the movable part 3.

FIG. 4 shows a tire forming mold according to a third embodiment of thepresent invention. The present embodiment is carried out by modifying,in another manner, the structure by which the movable part is fitted tothe mold main body. In FIG. 4, the same reference numerals are affixedto constituent components which are the same as those in FIGS. 1 and 2,and detailed descriptions for such constituent components will beomitted.

In FIG. 4, the structure by which the movable part 3 is fitted to themold main body 2 is as follows. Specifically, the mold main body 2includes the hollow portion 6 in a part of the tread forming surface 4in the direction of the circumference thereof, the hollow portion 6being one in which the movable part 3 is arranged. An inclined surface 9which is inclined with respect to the direction of the tire axis isformed in the hollow portion 6 of the mold main body 2, and the movablepart 3 is mounted slidably along the inclined surface 9 in the directionof the tire axis. For example, a dovetail groove can be processed in theinclined surface 9, and a projecting portion to engage with the dovetailgroove can be provided in the movable part 3. In addition, the movablepart 3 is designed to be displaced freely without a power between aposition (shown by a solid line) where the tire forming mold is closedand the other position (shown by a broken line) where the movable part 3is positioned when the tire is separated from the tire forming mold.

In the aforementioned tire forming mold, the movable part 3 is fixedwith respect to the mold main body 2 by a tightening force of the otherhalf of the tire forming mold while the tire forming mold is beingclosed. Thereby, a state that the movable part 3 complements the treadforming surface 4 (shown by the solid line) is brought about. The otherhalf of the tire forming mold is removed after completion of curing, andthe tire T which has been cured is elevated. At this time, the movablepart 3 is released from the tightening force which the movable part 3has received from the other half of the tire forming mold, and themovable part 3 is in a movable state. For this reason, the movable part3 slides along the inclined surface 9 inward (upward in FIG. 4) in thedirection of the tire axis as the tire T is elevated upper. In otherwords, the tire T is easy to be locally separated from the lower half ofthe tire forming mold in the area of the movable part 3. As a result,this can prevent concentration of stress on the tread portion of thetire T, which is caused due to groove forming ribs 5 a and 5 b arrangedon the tread forming surface 4. Accordingly, the ribs and blocks can beeffectively prevented from being damaged when the tire is removed.

FIG. 5 shows a tire forming mold according to a fourth embodiment of thepresent invention. The present embodiment is carried out by modifying,in yet another manner, the structure by which the movable part is fittedto the mold main body. In FIG. 5, the same reference numerals areaffixed to constituent components which are the same as those in FIGS. 1and 2, and detailed descriptions for such constituent components will beomitted.

In FIG. 5, the structure by which the movable part 3 is fitted to themold main body 2 is as follows. Specifically, the mold main body 2includes the hollow portion 6 in a part of the tread forming surface 4in the direction of the circumference thereof, the hollow portion 6being one in which the movable part 3 is arranged. An inclined surface10 which is inclined with respect to the direction of the tire diameteris formed in the hollow portion 6 of the mold main body 2, and themovable part 3 is mounted slidably along the inclined surface 10 in thedirection of the tire diameter. For example, a dovetail groove can beprocessed in the inclined surface 10, and a projecting portion to engagewith the dovetail groove can be provided in the movable part 3. Inaddition, the movable part 3 is designed to be displaced freely withouta power between a position (shown by a solid line) where the tireforming mold is closed and the other position (shown by a broken line)where the movable part 3 is positioned when the tire is separated fromthe tire forming mold. Incidentally, the plurality of groove formingribs 5 a extending in the direction of the tire circumference and theplurality of groove forming ribs 5 b extending in the direction of thetire width are arranged in the tread forming surface 4. Out of those,the groove forming ribs 5 a are formed in the movable part 3, and thegroove forming ribs 5 b are formed in the mold main body 2.

In the aforementioned tire forming mold, the movable part 3 is fixedwith respect to the mold main body 2 by a tightening force of the otherhalf of the tire forming mold while the tire forming mold is beingclosed. Thereby, a state that the movable part 3 complements the treadforming surface 4 (shown by the solid line) is brought about. The otherhalf of the tire forming mold is removed after completion of curing, andthe tire T which has been cured is elevated. At this time, the movablepart 3 is released from the tightening force which the movable part 3has received from the other half of the tire forming mold, and themovable part 3 is in a movable state. For this reason, the movable part3 slides along the inclined surface 10 outward in the direction of thetire diameter as the tire T is elevated upper. In other words, the tireT is easy to be locally separated from the lower half of the tireforming mold in the movable part 3. As a result, this can preventconcentration of stress on the tread portion of the tire T, which iscaused due to groove forming ribs 5 a and 5 b arranged on the treadforming surface 4. Accordingly, the ribs and blocks can be effectivelyprevented from being damaged when the tire is removed.

FIG. 6 shows a tire forming mold according to a fifth embodiment of thepresent invention. The present embodiment is carried out by modifying,in still another manner, the structure by which the movable part isfitted to the mold main body. In FIG. 6, the same reference numerals areaffixed to constituent components which are the same as those in FIGS. 1and 2, and detailed descriptions for such constituent components will beomitted.

In FIG. 6, the structure by which the movable part 3 is fitted to themold main body 2 is as follows. Specifically, the mold main body 2includes the hollow portion 6 in a part of the tread forming surface 4in the direction of the circumference thereof, the hollow portion 6being one in which the movable part 3 is arranged. An inclined surface10 which is inclined with respect to the direction of the tire diameteris formed in the hollow portion 6 of the mold main body 2, and themovable part 3 is mounted slidably along the inclined surface 10 in thedirection of the tire diameter. For example, a dovetail groove can beprocessed in the inclined surface 10, and a projecting portion to engagewith the dovetail groove can be provided in the movable part 3. Inaddition, the movable part 3 is designed to be displaced freely withouta power between a position (shown by a solid line) where the tireforming mold is closed and the other position (shown by a broken line)where the movable part 3 is positioned when the tire is separated fromthe tire forming mold. Incidentally, the movable part 3 extends from thebead portion to the tread portion of the tire T.

In the aforementioned tire forming mold, the movable part 3 is fixedwith respect to the mold main body 2 by a tightening force of the otherhalf of the tire forming mold while the mold is being closed. Thereby, astate that the movable part 3 complements the tread forming surface 4(shown by the solid line) is brought about. The other half of the tireforming mold is removed after completion of curing, and the tire T whichhas been cured is elevated. At this time, the movable part 3 is releasedfrom the tightening force which the movable part 3 has received from theother half of the tire forming mold, and the movable part 3 is in amovable state. For this reason, the movable part 3 slides along theinclined surface 10 outward in the direction of the tire diameter as thetire T is elevated upper. In other words, the tire T is easy to belocally separated from the lower half of the tire forming mold in themovable part 3. As a result, this can prevent concentration of stress onthe tread portion of the tire T, which is caused due to groove formingribs 5 a and 5 b arranged on the tread forming surface 4. Accordingly,the ribs and blocks can be effectively prevented from being damaged whenthe tire is removed.

With regard to the above described tire forming molds of the respectiveembodiments, only the movable part 3 constituting a part of the treadforming surface 4 in the direction of the circumference thereof is addedto the mold main body 2 for forming most parts of one side of the tireT. Furthermore, a special power is not required. For these reasons, thestructures of the respective tire forming molds as a whole are simple.This makes it possible to provide the tire forming mold which isinexpensive compared with the sectional type of tire forming mold, andthis enables costs for related facilities to be inhibited fromincreasing. Since the aforementioned tire forming molds have a goodreleasability, it is a matter of course that the tread compound needsnot be changed, a shape of the grooves needs not be modified, and theinner surface of the tire forming mold needs not be processed withresin.

Each of the aforementioned embodiments has been described by citing theexample that the present invention is applied to the lower half of thetwo-division type of tire forming mold which is divided into the upperand lower halves. Instead, the present invention can be applied to theupper half or the like of the two-division type of tire forming moldwhich is divided into the upper and lower halves.

Detailed descriptions have been given above of the preferred embodimentsof the present invention. It should be understood that variousmodifications, substitutions and replacements can be made as long asthese modifications, substitutions and replacements do not depart fromthe spirit or scope of the present invention defined in the appendedclaims.

1. A tire forming mold, which is a two-division type of tire formingmold, comprising: a mold main body for forming one side of a tire,wherein the mold main body consists of a hollow portion, and a single,freely displaceable movable part set in the hollow portion, the movablepart constituting a pan of a tread forming surface in the direction ofthe circumference thereof while the tire forming mold is being closed,and which can be moved while the tire is being removed from the tireforming mold, and wherein the movable part is mounted slidably along aninclined surface which is inclined with respect to the direction of thetire axis.
 2. The tire forming mold according to claim 1, wherein themeasurement of the movable part is one eighth to a half of thecircumferential length of the tread forming surface.
 3. The tire formingmold according to claim 1, wherein the behavior of the movable part isrestricted by a tightening force of the other half of the tire formingmold which is opposite to the movable part while the tire forming moldis being closed.
 4. A pneumatic tire producing method, wherein a tire iscured by use of the tire forming mold according to claim 1, and the tirewhich has been cured is removed from the mold main body comprising themovable part.